Investigation of alpha(2)/gamma phase transformation mechanism under the interaction of dislocation with lamellar interface in primary creep of lamellar TiAl alloys

Abstract

Under creep condition, the microstructural behavior of lamellar TiAl alloy is different from that of general materials. At as-received state, the amount of initial dislocations is very high and intrinsic dislocations, (b) over right arrow <110>. are existed in lamellar of dislocation density in gamma matrix is rapidly interface with irregular interface morphology. In early primary stage. the amount decreased. These dislocations are gliding on lamellar interface during primary creep. When they reach interface ledge, atomistic deformation caused by gliding dislocations can change the stacking sequence and the composition of a-ledge. As a result of this process, alpha(2), is transformed to gamma phase. During this phase transformation process. a new unstable phase. Ti2Al, is observed. This new phase is intermediate and disordered phase between alpha(2) and gamma ordered phases. The atomistic model for alpha(2) --> Ti2Al -->gamma phase transformation process is newly proposed. (C) 2002 Elsevier Science B.V. All rialits reserved.